In recent years there has been increasing need for industrial gases, such as oxygen and nitrogen for example, in such diverse applications as steel making, aluminum production, pharmaceutical production and glass making. Although gases for such applications have conventionally been supplied by vaporizing liquid ("bulk") oxygen or bulk nitrogen stored on site in cryogenic storage vessels, it is often more cost effective to generate such gases using on-site vacuum and/or pressure swing adsorption (V/PSA) air separation systems or membrane air separation systems.
To assure uninterrupted gas supply, such on-site gas generating systems typically use vaporized liquid to replace (i.e. back up) the on-site generated gas in the event of a gas generating system outage due to electric power interruption, mechanical failure, etc. In addition, such liquid vaporizing systems are also used to supplement the on-site generated gas flow when the application's gas requirement exceeds on-site plant capacity. Unfortunately, compositional differences between the on-site generated gas and the back-up/supplemental vaporized liquefied gas can render the gas supply system unsuitable for some applications, thereby preventing them from realizing the lower costs associated with using on-site generated gases. When, for example, V/PSA oxygen product, which is typically between 90 and 95 volume percent (vol. %) oxygen (the balance being substantially nitrogen and argon), is backed up using liquid oxygen, which is typically at least 99.5 vol. % oxygen, the oxygen concentration in the product from the gas supply facility can suddenly change by between 4.5 and 10 vol. % during a V/PSA plant outage.
An example of an application where such a substantial or material change in oxygen concentration is unacceptable is in glass finishing. Such operations include glass forming, polishing, edge-firing, glazing and quartzworking, and typically use many oxy-fuel burners which are set up using manual combustion controls. In such operations the above described fluctuations in the oxygen concentration of the combustion oxidant can cause changes in flame temperature thereby influencing glass formability, and changes in flame stoichiometry, which affects the color of certain glasses. While it may be possible to adjust the ongoing combustion process to compensate for oxidant compositional changes, this is often operationally impractical due to numerous manual controls, a limited number of operator personnel, and/or little or no advanced notice of the oxidant change.
Thus there is a need in the art for a highly reliable, cost-effective means to back up or supplement non-cryogenic on-site gas supply systems serving composition-sensitive applications.